MIMO (multiple input, multiple output) is a wireless communication scheme in which multiple antennas and transceivers are used to increase the reliability of data transmission. Data from different communication chains at each end of a communications circuit are combined to minimize errors and optimize data speed. Other types of wireless communication schemes include MISO (multiple input, single output) and SIMO (single input, multiple output).
In conventional wireless communications, a single antenna is used at the transmitter and another single antenna is used at the receiver (e.g., single input, single output or a SISO system). In some cases, this gives rise to problems with multi-path effects. For example, when an electromagnetic wave hits obstacles such as hills, canyons, buildings, utility wires, and/or walls or furniture in an indoor environment, the wave-fronts are scattered, and thus may take many paths to reach the destination. The late arrival of scattered portions of the signal may cause problems such as fading, cut-out (i.e., cliff effect), and/or intermittent reception. In digital communications systems such as wireless Internet, these problems can cause a reduction in data speed and an increase in the number of errors. The use of two or more antennas, along with the transmission of multiple signals (one for each antenna) at the transmitter and the receiver, may reduce the problems caused by multi-path wave propagation.
Data in a MIMO system can be sent by a single or multiple streams. In a single stream, the same data are sent through multiple transceiver chains. When data are sent by multiple streams, data are divided into data packets and sent through different transceiver chains. In general, the capacity of a MIMO system increases linearly as the number of transceiver chains increase. One of the important concerns in designing a MIMO system includes reducing signal correlation between two or more transceiver chains.
One solution addressing this concern can be referred to as polarization diversity. Polarization is a property of waves that describes the orientation of their oscillations. Polarization diversity generally involves implementing antennas having different polarizations at the transmitter. An antenna may be configured to have any one of vertical, horizontal, cross, or left or right handed circular polarization. During data transmission, especially when the transmitter and receiver are far apart, a matching antenna polarization at both ends is generally optimal for data transmission. Existing wireless communication systems employing antenna polarization diversity typically implement multiple antennas at the transmitter in varied but fixed polarizations. The fixed antenna polarizations generally cannot be adjusted during transmission of a data stream.
Thus, a market exists for a wireless communication system that is enabled to dynamically adjust antenna polarization during data transmission.